Kenyan-born University of Otago PhD researcher Bonface
Manono prepares to return to his home country after
completing research on aspects of dairy farming
sustainability. Photo by Peter McIntosh.
Spreading cowshed effluent on fields and and undertaking
irrigation are improving soil quality on dairy farms, a
University of Otago PhD student, Bonface Manono, says.
Mr Manono recently completed his PhD research, which involved
studying soil quality at 41 farms in the Waitaki district,
most of them shareholders in the Morven, Glenavy, Ikawai
Irrigation Co (MGI).
MGI funded the study, along with the Agriculture Research
Group on Sustainability (Argos), and Otago University.
A PhD student at Otago University's Centre for
Sustainability, Mr Manono has been working with MGI farmers
over the past three years to measure changes in soil quality,
and especially earthworms in paddocks which were irrigated or
received effluent collected from the farmyards and cowsheds.
It was ''great news'' that farmers were recycling nutrients
by spreading the effluent back on the paddocks, and were also
building soil quality.
''So they will need less fertilisers and irrigation water in
the longer run,'' he noted.
About 10% of the cows' urine and faeces was deposited in farm
yards and the cowshed. Dairy farmers were getting smarter and
finding better ways of spreading the waste back on to the
land to reduce waste and environmental risks, he said.
The numbers of top- and mid-level earthworms in irrigated
soil were increasing in irrigated paddocks and where effluent
was spread, he had found.
Earthworms were what ecologists called ''ecosystem
engineers'' because ''they make and maintain soil, promote
nutrient turnover and help plants take up nutrients'', he
''Healthy soil has lots of earthworms,'' he said.
It was ''great'' that irrigation and effluent spreading built
earthworm numbers in the upper and mid-levels of the soil.
'' But it is also a bit worrying that we also found that
deep-dwelling earthworms declined in irrigated paddocks,
perhaps because they are being drowned in the very wet
conditions,'' he said.
''We need to go looking for other species that can cope
better with saturated soils to keep the soil healthy in the
longer run,'' he said.
Prof Henrik Moller, of the Otago centre, was Mr Manono's
supervisor, and is science leader of the New Zealand
Sustainability Dashboard Project, which directed this
Mr Manono had worked hard and his research findings were
nationally significant, in highlighting some of the benefits
of effluent recycling on dairy farms, Prof Moller said.
Such recycling had many advantages, including reducing the
amount of costly externally sourced fertiliser.
Substantial amounts of energy were required to manufacture
such fertiliser, and recycling effluent was more efficient
and helped improve soil health.
The health of earthworms and of beneficial microorganisms in
the top 30cm of farm soils was of crucial importance for the
New Zealand economy, he said.
Robin Murphy, chairman of MGI, said the research was good
news for the sustainability of dairy farming.
''Effluent spreading and irrigation build soil structure, so
the soils can hold more water and be better aerated.
''The treated soils also have higher nutrient levels. So all
up, effluent spreading and irrigation itself is making
farming more efficient,'' he said.
''Our survey showed that our farmers put a high priority on
soil care, right up there with stock welfare and production
efficiency as farm management priorities,'' he said.